A FSCM may be included in various systems for monitoring whether an oscillator or a clock has failed. Oscillators may include oscillators internal or external to a chip, die, processor, or other electronic device. Internal oscillators may be R-C based and therefore have high tolerances and low temperature stability. External oscillators may be circuit-based, quartz-based, or crystal-based, and a signal from the oscillator may be routed to an external pin of the electronic device. External oscillators may be more reliable, stable, and precise sources of clock frequency, but may be subject to assembly errors and printed circuit board damage.
Oscillators may experience various faults. For example, an oscillator may fail to start up, may fail to lock into phase, or may experience a power failure. A connection from the oscillator to its intended targets may fail and thus the oscillator may merely appear to fail. Load capacitance may cause faults. Each quartz crystal may be designed for a specific load capacitance. Capacitors may be used between a pin of the quartz crystal and ground. During oscillation, electric charge flows from a capacitor through the quartz and into another and back again. The attached capacitors may need to match the crystal's internal capacitance for a stable and precise oscillation. Given a specific load capacitance identified by designers of the oscillators, the crystal may oscillate with the specified frequency. If the load is too low, the crystal might not start oscillating, as there is insufficient electric charge to oscillate between the capacitors and the crystals. If the load is too high, the voltage swing of the oscillation may be reduced because of the additional charge in the capacitors that cannot flow through the crystal. A pin can form a parasitic capacitance, which can increase if sockets are used. The copper lines or leads of a printed circuit board can add parasitic capacitance. These capacitances might need to be subtracted from the load capacitors' values to match the required load. If parasitic capacitance increases or decreases, performance of the crystal may suffer.